Ay, but to die, and go we know not where;
To lie in cold obstruction and to rot;
This sensible warm motion to become
A kneaded clod; and the delighted spirit
To bathe in fiery floods, or to reside
In thrilling region of thick-ribbed ice;
To be imprison’d in the viewless winds,
And blown with restless violence round about
The pendent world; or to be worse than worst
Of those that lawless and incertain thought
Imagine howling: ’tis too horrible!

(from Measure for Measure)

The question concerns the interpretation of the last two lines (I kept the rest to give some context). What is the subject of imagine in the last line? At first glance it would appear to be those from the penultimate one, but if so, what were the things thought lawless and incertain? And if imagine is just an exhortation to the reader, what does the penultimate line mean? Some suggestions:

-how lawless and incertain to imagine one’s own future to be “worse than worst” of those in the aforementioned scenario; imagine the howls of those who end up in Hell

-it is too horrible to endure even worse than the imaginings of those of lawless and incertain thought which manifest themselves as howling

-it would be too horrible to imagine the howling of those who, when they lived, were of lawless and incertain thought

-to suffer worse than those who according to people’s lawless and incertain thoughts howl in Hell; something altogether too horrible

The last is perhaps closest to the mark. The picture becomes clearer if you replace “thought” with “thoughts”. I guess it was possible to contract like that in Shakespeare’s time, the expansion being “lawless thought and incertain thought”.